Increasing energy demands have driven increased interest in the development of alternative energy technology. Renewable energies are attractive alternative energy sources due to their cleanness and unlimited availability. Renewable energies include solar energy, thermal radiation energy, and various vibration energies.
Piezoelectric materials have been used to harvest vibration energy from the environment. Applying a mechanical stress to a piezoelectric material produces electric polarization in the material resulting in the generation of a voltage across the piezoelectric material. Piezoelectric electromechanical transducers convert mechanical energy to electrical energy. MEMS (microelectromechanical systems) piezoelectric cantilever devices capture environmental vibration energy and convert it to electrical energy. MEMS are very small devices having overall sizes ranging from twenty micrometers to one millimeter. The components of MEMS devices are usually between one and one hundred micrometers in size.
Photovoltaic cells convert solar energy into electrical energy. However, existing photovoltaic cells have low efficiencies. For example, commercially available single crystal silicon-based photovoltaic devices convert solar energy into electrical power with efficiencies of only fifteen percent.
Carbon nanotube films exhibit near blackbody properties. Carbon nanotubes efficiently absorb electromagnetic radiation and convert it into heat.
Each of the existing technologies for harvesting renewable energies is only capable of absorbing one form of energy. Photovoltaic cells convert solar energy into electrical energy, while aligned zinc oxide nanowire arrays and MEMS piezoelectric cantilever devices convert mechanical energy into electrical energy.